MIM parts

I'm seeking the wisdom of the forum. I hear a lot of criticism of the use of MIM parts, especially in discussions of 1911's. What's the story on this? I understand the appeal of hand craftsmanship, but I just can't help believe that some of the highest quality consumer goods in the world (Honda Accords and Goldwings come to mind) are mainly put together with modern manufacturing techniques.

Is the MIM thing the subject of myth, or is there a real history of catastrophic failure of these parts on a wide scale? Any enlightenment you folks can provide will be much appreciated.

I believe that Packard is our resident metallurgist.
Maybe he'll have an answer.

I have a general faith in manufacturers, that nobody truly wants to make a defective product (except, maybe, the Chinese).
Thus, I am willing to bet that well-designed, well-made MIM parts are the equal of forged-and-machined ones—in the applications for which they have been designed. However, if Taurus uses MIM parts, they are probably not the very best choice.

I don't have any experience with the products itself, but I understand the process.

With metal injection molding you take powdered metal (usually stainless steel) mix it up with molten plastic resin, and mold it in a plastic injection molding machine. It will look like metal. It's properties will not be the same.

The parts may be fully suited for the applications that they are designed for. Much like the doubt we had (years ago) about the resin frames on Glocks, there will be doubts about MIM.

I don't have a problem with the process so much as I have a problem with the name. We have "fiberglass reinforced nylon" injection molded parts that display incredible strength. They are 50% long fiber along with the nylon. I've seen at a shot show, a knife molded of this material and the demostrator used a mallet to drive the point of the knife through a 3/4" thick piece of plywood. Clearly this is an acceptable application for a dagger (especially if you want to get past airport security).

I don't know the proportions of steel to resin for MIM, and I don't know the resin being used (but I will look it up). But in my mind this is "metal reinforced plastic" and not "metal injection molded" parts.

I would imagine that the metal improves the wear characteristics, but the strength comes from the resin. Unlike the fiberglass whose long fibers reinforce the nylon, the metal does not. So I would imagine that the characteristics of the resin will control the characteristics of the MIM parts.

I will do some reading and get back to you.

Addendum:

My understanding of this process as described above was incorrect.

The basic process begins as I described it with a very high percentage of metal combined with the binder (resin).

After the part has cooled the binder is carefully removed from the parts. As the powder has no binder at this point it is very fragile. The binder can be removed with solvent or by heat (melting the plastic).

After the parts are free of the binder they are sintered (pressed under high pressure) to bind the metal (or heated to bind the material). At that point it is treated as though it was a metal part.

Conventional steel (billet) has a grain that runs in one direction. It is considerably stronger in the direction of the grain than it is across the grain. So when you machine away material (say at the trigger guard) part of the thinned guard is going the direction of the grain; and part is not. It is as though you machined it from wood. So the sections that have the short lengths of grain will be substantially weaker than the sections with the longer lengths.

Steel can be forged (struck with a heavy force at a high heat), and if the forging die is designed correctly you can have the grain flow in various directions (like water would flow). If it is designed correctly you could have the grain follow the contour of the trigger guard and it would be equally strong in all sections. That is why forging adds so much to the quality of a weapon. It allows thinner sections (and lighter weight) with equivalent strength.

Sintered metal has been used for many more years than MIM has been in existence. I've never heard of any forging done on sintered metal; I don't know if sintered metal has a grain like cast or rolled metal does.

So is MIM any good? It all depends upon the engineering behind the parts. If the parts that are MIM are chosen carefully and designed thoughtfully they should do OK. They are certainly less expensive to produce.

The risk for the MIM industry is that someone will choose an inappropriate part to MIM and it will cast a gray cloud over the entire process.

Imagine for example if the early Glocks suffered frame failures. If that had happened, do you imagine there would be all these resin framed guns that we see today? I don't. But the Glocks were well designed and the resin was used in appropriate situations (and steel where it was required).

The difference is that when Glock came out with the plastic framed guns the process of plastic injection molding was well-established. On the other hand, the MIM process is still evolving. So that the parts that are MIM today may not be of the same quality as MIM parts produced 5 years from now. Time will tell.

I will stick my neck out here and state that for most applications the MIM parts that are being used today will prove acceptable. When they don't, the manufacturer will re-call the guns and replace the offending parts with parts that were produced using more conventional methods.

The comment about steel (in general) having a grain direction that is considerably stronger in one direction is new info to me. While I work primarily with structural steel (beams, columns, angles, etc) and not stainless, I haven't seen anything in the design properties, material testing, or code books referencing a strong and weak axis of structural steel. (there certainly is for wood though).

I've heard about grain size having an effect on the overall strength or durability of the steel, but not a difference in any one direction.

It depends. Some manufactures have had issues with MIM parts failures, Para Ordnance and Kimber seem to be the whipping boys for MIM failure.

Almost all of the mid tier 1911 makers such as Colt, Kimber, Springfield, Smith & Wesson, etc use MIM parts to some extent, more some than others and on differing parts. Personally, I find that tool steel parts seem to have a better fit & finish, appearance. The MIM just looks different on some parts. I do not like MIM slide stops and thumb safeties, even though I currently have a high end 1911 with a MIM (Kimber) thumb safety. I have only had one MIM part failure and that was due to a combination of errors on the manufactures end.

I think MIM parts are good in some applications, but not all. In addition to no MIM slide stops, I want my ignition components made from steel.

In short, not all MIM is created equal.

Of the mid-grade 1911s, Dan Wesson uses no MIM if I recall correctly, and Sig used to be all steel, but I recall reading somewhere that even they are using some MIM parts now.

There's a thread on another forum where someone took a tool-steel part and MIM part and put them under a high power microscope and you could see "voids" (Air pockets) in the MIM part that were not present in the steel part, granted these pockets are tiny as hell, but they're still there.

The comment about steel (in general) having a grain direction that is considerably stronger in one direction is new info to me. While I work primarily with structural steel (beams, columns, angles, etc) and not stainless, I haven't seen anything in the design properties, material testing, or code books referencing a strong and weak axis of structural steel. (there certainly is for wood though).

I've heard about grain size having an effect on the overall strength or durability of the steel, but not a difference in any one direction.

Do you have any info on this topic?

Metal grain follows the direction in which it was rolled. Forged grain follows the direction of the contours (in general).

If you consider a simple 1/4-20 screw thread, if it is a cut thread (that is, you start with .250" diameter wire and cut the threads on a lathe) then you are interrupting the grain of the metal with each cut.

If you are producing a rolled thread to 1/4-20 you would start with .212" diameter wire and as you roll the thread into the metal it also grows in diameter. It is as though you had a big glob of clay and you squeezed it in your fist. It would get smaller where your fingers squeezed, but it would extrude out between your fingers. In a thread like this the grain follows the undulations of the thread and they are much stronger than cut threads.

On your steel beams the grain would be lengthwise.

On sheet metal it is easier to fold the metal along the grain than it is against the grain.

Federal-Mogol, a diesel component manufacturer came to our company a while back for some 4" diameter rings made from wire that measured .120" in diameter and the ends were welded. They were using a 4" diameter ring stamped from flat steel that was .120" thick. They used this ring to press into the head gasket on a diesel engine and create a good seal. But the rings were blowing out. The grain was all going one direction and at the weakest point it would blow out. The wire rings, on the other hand, had the grain running the length of the wire, which we then rolled into a ring and welded. As long as our weld was homogenous with the rest of the grain there was no weak point and the rings would not blow out.

Grain direction is specified for some stampings we produce and it has to be taken into consideration when designing the tooling.

Grain direction is particularly important when profiles are small, and the stresses are high. I would imagine that weapons like the Scandium J-frame would not exist if they could not be forged.

Also many rifles and shotguns have forged receivers. And hammer forged barrels.

But for many products the grain direction is not an issue and can easily be ignored.

The early use of new technology is fraught with risks (and huge paybacks).

Consider the AMT Backup. This weapon was designed around the investment casting technique. Virtually every part of the gun was investment cast (except the springs and the barrel). There were some early problems that grew exponentially because the factory went into over-drive attempting to fill all the orders.

Eventually the entire industry adopted investment casting for at least some of the components. Until AMT used the technique it was almost exclusively used for jewelry manufacture casting soft metals like gold and silver.

When Glock made his plastic guns the molding industry was mature and there was a vast body of knowledge out there on the process and the properties of the molded parts.

In my mind MIM more nearly mimics the situation AMT faced. I think there will be some mistakes on components, but since the frames and barrels are not going to be affected you might see recalls on parts like the slide locks, or safety or some other lightly stressed small part. Once the bugs are worked out and the components see wide use in the industry then the specialty components from people like Wilson will take on additional glamour.

Personally, I am not an early adopter of new techniques (though I don't shoot black powder). I like to see some track record before I jump in. For me, Glock has just proven itself. 25 years seems like a reasonable time frame for testing an idea.

Although it isn't a perfect analogy, it reminds me of the early use of coated cylinder bores in the automotive and motorcycle industries, which gave decidedly mixed results for a while. More recently, though, some of those engines have turned out to be just about bullet proof. I guess there's a learning curve with most things.

Although it isn't a perfect analogy, it reminds me of the early use of coated cylinder bores in the automotive and motorcycle industries, which gave decidedly mixed results for a while. More recently, though, some of those engines have turned out to be just about bullet proof. I guess there's a learning curve with most things.

I don't think they so much gave mixed results as much as the technique was properly specified in some instances and improperly specified in others.

Race engines do eliminate the cast iron sleeves that production engines use. In place of that they "hard anodize" the cylinders. We normally look at anodizing as a decorative finish, but it is not a finish that sits on the surface of the aluminum, but rather it penetrates the material itself. As it penetrates the aluminum it makes the surface harder. The longer you leave the aluminum in the annodizing solution, the greater the depth of the penetration. So for an engine that is going to run 500 miles in a race this makes sense. It allows improved heat transfer and allows more accurate machining. But when GM tried to use the same technique in the Vega engines of the late 1970s the engines failed like crazy.

So in the race cars the hard anodizing was properly specified; in the Vega it was not. Note: You can anodize aluminum only; anodizing will not work on any other material.

As kids many of us built plastic model cars. These kits came with "chrome" plated parts which were actually vacuum metalized (covered with aluminum). For this application it is fine. For reflectors on low temperature lamps in cars it is fine too. But when they tried to replace door knobs and radio knobs with these the aluminum wore off in just months.

So in most cases when a new technique fails it is not the technique that is at fault, but the engineering. I poorly chosen part for a specific manufacturing method dooms the part to fail.

...And, the AMT Backup was not a complete failure.
The investment-cast parts of mine seem to be holding up quite well.
The only problems I've experienced with it were due to incomplete attention to finishing and detail work. Had AMT slowed down a bit and done their detailing better, it probably would've been a popular series of weapons.

(It took very little kitchen-gunsmithing time, to clean up the jobs that AMT didn't properly finish. But a new-gun buyer should not be saddled with the manufacturer's clean-up work.)

...And, the AMT Backup was not a complete failure.
The investment-cast parts of mine seem to be holding up quite well.
The only problems I've experienced with it were due to incomplete attention to finishing and detail work. Had AMT slowed down a bit and done their detailing better, it probably would've been a popular series of weapons.

(It took very little kitchen-gunsmithing time, to clean up the jobs that AMT didn't properly finish. But a new-gun buyer should not be saddled with the manufacturer's clean-up work.)

AMT's failure was not in the gun design (though there were some early problems) but in the management. At the time the .380 Back Up in all stainless steel was a bargain, and for the time, super-compact. The problem was that they got so busy so fast that they spent all their energy building new guns and none of their energy correcting the problems.

At one point they were purportedly working 24/7 to keep up with orders.

I agree, if they had taken a step back and worked out all the details they would have been way ahead of the game.

Not only was the manufurting method very forward thinking, the original concept of a small, pocketable .380 in all stainless steel was very forward thinking.

Stainless steel is very much more difficult to machine than is carbon steel. At that time carbide cutting tools were not very good and did not last very long. Amost all stainless steel weapons were machined from heavy forgings that they shared with the carbon steel versions. Because of the difficulty machining stainless steel the original stainless guns were more than double the cost of the carbon steel versions.

AMT changed all that. Other manufacturers saw that they could investment cast frames and then finish the balance of the machining with minimal amouts of work.

Investment castings can hold tolerances of +/- maybe .020" so the machining would only have to remove about .015" or .020" maximum--a single pass of the tool will accomplish that.

I used AMT as an example only because they were using a relatively untried process for handgun manufacturing much like MIM embracers are doing now. If the current crop learns from AMT's early mistakes they can do a lot better.

Note: A friend of mine ordered his .380 Back Up at the same time I did. His functioned perfectly and he kept it for several years. I could never get mine to work as well and customer service was quoting 6 to 9 month turn around on repairs. I had the gunsmith try to fix mine a couple of times but then I finally gave up and bought a .38 Centential Airweight to replace it.

But on mine, even if I were patient enough to wait for the factory to resolve the firing pin problems, the sights were not what I wanted in a gun. They were no better than the snub nosed revolver--just a groove in the top of the slide. So I was not that enamored with the weapon even when it worked. I probably would have traded it is at some point over that issue.

I'm trying to remember if I traded that gun in on my Walther PPKS or my Airweight Centennial. I think it was the Walther over the issue of the sights. The Walther has real sights.

Also, mine was a striker fired single action pistol. I think they changed to double action only later on.

High Standard is the current distributor; I don't know if Arcadia Tool and Machine is the current manufacturer or if High Standard took that over too.

My .45 Backup also has only a groove along the top of its slide, to serve as a sight.
Nevertheless, it's quite accurate, out as far as I can reliably hit: About 20 yards. That includes head shots.
At these short, save-your-life ranges, an experienced shooter can hit without using sights at all. It's called "slide shooting," and all it requires is practice.

So maybe here endeth this short foray into thread hijacking.
Can we now return to the regularly-scheduled thread?

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